Folding stairway



Sept. P -V .HARMON FOLDING STAIRWAY I Filed Sept. 15, 1954 2Sheets-Sheet 1 INVENTOR. PA 04. M f/A EMU/V A TT'OENEY' Unite rornnsosrAmwAY Paul V. Harmon, Nashville, Tenn., assignor to Precision PartsCorporation, Nashville, Tenn, a carpet-anon of Tennessee ApplicationSeptember 13, 1954, Serial No. 455,510

Claims. ((11. 22848) This invention relates to folding Stairways.

It is common practice to provide folding and so-called disappearingstairways for providing convenient access to the attics of houseswithout the loss of floor space accompanying the use of permanentstairs. Such folding stairways usually have sectional stair units whichare extended in alinement with each other when the stair is unfolded foruse, and which sections are folded one upon another when the stair ismoved upwardly into the ceiling frame when not in use.

Folding stairways of this type employ various types of counterbalancingmeans for holding the stairs in inoperative positions when not in use.Most constructions of this kind employ springs as the counterbalancingmeans, these springs being efiective for holding the parts inoperativewhen the stair sections are folded, thus shortening the lever armtending to swing the stairway downwardly. When the stairway is inunfolded or operative position, the effective lever length of the stairunit overcomes the tension of the counterbalancing spring, such springfre quently having its connections with the stairway so arranged as tobe inefiective for transmitting any lifting force to the stairway whenunfolded.

When a stair of this type is unfolded and the parts are in operativepositions, it is necessary to provide some form of support for the upperstair section. This usually is accomplished by linkage connecting theupper stair section to the ceiling frame. Such linkage connectionsusually provide at each side of the stairway two links connected to eachother and having their remote ends connected respectively to the upperstair section of the ceiling frame. In the absence of some meansspecifically provided for such purpose, the weight of the parts willcause the links at opposite sides of the stair to assume dead-centerpositions, thus making it necessary to break the hinged connectionsbetween the pairs of links before the stair can be folded. Thisdisadvantage has been overcome by causing the counterbalancing springsto be bent and thus substantially distorted to exert a turning force onthe upper links to break the links from deadcenter positions. Such anarrangement shortens the life of the springs and renders the stair noisyin operation. Other means employed for this purpose have been relativelyexpensive to manufacture.

An important-object of the present invention is to provide a foldingstair having stair sections, the upper of which is provided withsupporting link means to carry the load on the stair when the latter isunfolded, and to provide a highly novel and simplified means forpreventing the supporting links from assuming dead-center positions whenthe stair is to be folded.

A further object is to provide such a construction wherein the springcounterbalancing means exerts a direct straight-line pull under allconditions except when the stair is unfolded, in which case there is avery slight deflection imposed on the spring transversely of the line ofpull thereof, the spring tension thus being operative character justrefeired to wherein the stationary element to exert sufiicient turningforce on the upper links to throw slightly out of line the centerpivotal connections out effecting any distortion of the balancingsprings from their normal shapes.

A further object is to provide such a construction wherein the upperlink member on each side of the stair is in the form of a bell cranklever one arm of which has mechanical connection with one end of theassociated spring While the other end of each spring is connected to theceiling frame and to provide a stationary element supported by a ceilingframe and arranged slightly above the line between the end of eachspring connected to the bell crank lever and the end connected to theceiling frame when the stair is unfolded, under which conditions therewill be slight deflection-of each spring connection from its normal lineto exert a slight turning movement on each bell crank lever to preventthe link connections from occupying dead-center positions when the stairis ready to be folded.

A further object is to provide a construction of the for deflecting eachspring under the conditions referred to is a stud forming part of thepivotal support for each bell crank lever.

A further object is to provide such'a construction wherein a linkconnection is provided between the upper arm of each bell crank leverand the adjacent end of the spring for taking the transverse thrust oneach spring connection, thus eliminating the necessity for distortingeither spring out of line.

Other objects and advantages of the invention will become apparentduring the course of the following description.

In the drawings I have shown one embodiment of the invention. In thisshowing:

Figure l is a perspective view of the stairway showing the partsunfolded into operative positions,

Figure 2 is a substantially enlarged detail sectional view on line 2 -2.of Figure 1,

Figure 3 is a central vertical longitudinal sectional view through theceiling frame and upper portion of the stairway showing the latter inunfolded position, certain of the operating connections being shown indotted lines in the positions they will assume when the stair is folded,

Figure 4 is a similar sectional view showing the parts completelyfolded,

Figure 5 is an enlarged fragmentary sectional view on line 5-5 of Figure3, and

Figure 6 is an enlarged detail sectional view of one of the pivotalsupports for one of the bell crank levers, and associated parts.

Referring to the drawings, the numeral 10 designates a ceiling frame asa whole adapted to be fixed in the ceiling of a building in the usualmanner. tangular and includes transverse ends 11 and 12 and side members13.

The stair indicated as a whole by the numeral 16 is adapted to besupported by the frame 10 and to be folded thereinto when the structureis not in use. The stair 16 includes a plurality of sections 17, 18 and19, the first two of which are hinged to each other at 20 whereby thesection 18 folds upwardly in the position shown in Figure l to assume aposition over the section 17. The sections 18 and 19 are hinged togetheras at 21, and it will be apparent that in folding the sections, thesection 18 will swing relatively upwardly about the hinges 20 while thesection 19 swings relatively downwardly about.

This frame is recsuch plate (Figure the hinges 21, the sections thusassuming the folded positions shown in Figure 4.

A cover for the bottom of the frame is provided and is indicated by thenumeral 24. This cover fits into the bottom of the frame 10 when theparts are folded, as shown in Figure 4, and is hinged as at- 25 to theframe 10. The cover 24 is provided with batten strips 26 secured theretoat spaced points, and the ladder section 17 is secured in any suitablemanner to the batten strips.

Each of the ladder sections is provided with the usual steps 27connected between the side runners 2 5- cf the ladder sections. To eachside runner of the upper ladder section 17 is pivotally connected as at30, a link 31. Each side frame 13 carries a bell crank lever 32comprising a pair of arms 33 and 34. Each arm 33 forms in effect a linkpivotally connected at its lower end as at 35 to the upper end of one ofthe links 31. Each side frame 13 carries a plate 36 to which is attacheda pin 37 pivotally supporting the associated bell crank lever 32. Eachpin carries at its free end a head or stud 38 the annular surface ofwhich may be convexed as at 39 for a purpose to be described.

A counterbalancing spring assembly 42 is provided adjacent each sideframe member 13. Each such spring assembly comprises a tension spring 43having one end fixed to a plate 44 by means of an eye 45 carried by Bachplate 44 is arranged adjacent the frame member 12. The opposite end ofeach spring is connected as at 46 to a link or reach rod 47 and theother end of such rod or link is connected by a pin 48 to the arm 34 ofthe associated bell crank lever. The stud 38 is so arranged that whenthe parts are in the unfolded positions shown in Figures 1 and 3, thetop of the stud 38 is above a line between the associated eye 45 and pin48. Under such conditions, the rod or link 47 will be deflected upwardlyas clearly shown in Figure 3. It is preferred that the member 43 beformed of a steel rod or heavy steel wire, although it has been found inpractice that this member may be formed very readily of a piece of steelcable.

As stated, the parts when unfolded occupy the positions shown inFigure 1. To facilitate ascending the stair one of the side framemembers 28 of the ladder section 17 is preferably provided with a handrail 5i). This rail readily may be supported with respect to theadjacent side frame of the ladder section 17 by brackets 51.

Operation The parts normally occupy the positions shown in Figure 4. Theend of the cover 24 remote from the hinge is provided with some type ofhand grip (not shown) to facilitate pulling the stairway downwardly.Such hand grips are conventional. When the parts are in such positions,the springs 43 are positioned as shown in dotted lines in Figure 4,exerting a pull upon the arms 34 of the bell crank lever 32 whereby thepivot pins exert an upward force through links 31 to hold the ladderparts in folded positions.

When the ladder is to be used, the hand grip is pulled downwardly untilthe ladder section 17 and cover 24 assume the positions shown in Figures1 and 3. At this time, the sections 18 and 19 will be superimposed abovethe ladder section 37, remaining in the relative positions shown inFigure 4. The operator will grasp the lower step 27 of the laddersection 19 and pull to the right as viewed in Figures 1 and 3, thusunfolding the ladder sections to permit them to swing downwardly tooperative positions. Under such conditions, the lower ends of the sideframe members 23 of the ladder section i9 will engage the floor when theladder is ready for use.

As previously stated, the stud 33 constitutes a stationary elementcarried by each side frame 13 above a line drawn between the associatedeye and pivot pin 43. In the interest of achieving the greatest possiblesimplicity, this stationary element preferably is the stud 33 fixed tothe pivot pin 37. When the parts are in the folded position referred toabove, each spring unit 42 has its elements in alinernent from end toend. This alinement is preserved as the parts swing downwardly with thepivot pins 30 and 35 following the arcs shown in construction lines inFigure 3, until the operative positions of the parts are reached. As theladder sections approach positions in alinement with each other, eachrod 47 will bear upon the surface 39 of the associated stud, thusarresting downward movement of the portion of the rod 47 engaging thestud. The pivot pin 48 at each side of the frame wii} continue to movedownwardly to a slight extent, thns flexing the rod 47 upwardly as shownin Figure 3, assuming the rod to be made of flexible material. A rigidrod or a rod formed of a flexible cable, will serve substantiallyequally as well as a flexible steel rod.

ra'hcn the parts reach the positions referred to, each spring unit 42will have the parts thereof subjected to a force laterally of the normalline of the parts thereof and the tension of each spring, transmitted toits associated pin 43 above the axis of the pivoted pin 37, will exert aslight turning movement on the associated bell crank lever 32. Unlessthe ladder is occupied by a relatively heavy person, or a personcarrying a load on the stairway, the pivot pins 35 will occupy positionsslightly to the right in Figures 1 and 3 of a plane passing through theaxes of the pivot pins 30 and 37. Thus the pivot pins 35 will beprevented from assuming deadcenter positions relative to the pivot pins3% and 37.

in connection with the foregoing, it will be noted that a line betweenthe axis of the pin 48 and the point of contact of the link 47 with thestud 38 is at a slight angle to a line between the axes of the pins 37and 48. The positioning of the parts in the manner shown in Figure 3,therefore, preserves a short moment arm in the lever arm 34 whereby thespring tension exerted endwise through the link 47 exerts a slightturning movement of the bell crank lever 32. The deflection of thespring unit, moreover, causes the application to the pivot pin 48 of anupward component of force to assist in such turning movement. These twoforces in practice have been found adequate, even under rathersubstantial loads on the stairway, to maintain the pivot pin 35 at eachside of the stairway slightly out of a dead-center position for thepurpose stated.

If the stairway is being subjected to heavy weights, the pivot' pinsreferred to may swing approximately into alined or dead-centerpositions, further deflecting each spring unit from its normalstraight-line condition. When such heavy weight is released from thestairs, however, the pivot pins 35 will return to the approximatepositions shown in Figures 1 and 3. This permits the stairs to be foldedand there is no necessity for having to break the joint between thelinks 31 and the lever arms 33. This is accomplished without the use ofextra springs and without the necessity of having to bend or otherwisedistort the springs 43. Each of these springs is always straight fromend to end under all conditions. This fact prolongs the life of thesprings as compared with those constructions in which the springs arebent or distorted, and an occasional drop of oil at the points 45, 46and 43 (Figure 5) will prevent the occurrence of any annoying springnoises.

As previously stated, a heavy weight upon the stairs may swing thepivots 3!), 35 and 37 substantially into a common plane. However, thisdoes not noticeably affect the position of the stair 17. From Figure 3,it will be noted that if the pivot pins 35 move to the left to thealined positions referred to, the horizontal component of movement ofsuch pins will be accompanied by a downward vertical component ofmovement of the pivot pins 30 but the latter movement will be negligibleand will not be noticed by a person using the stairs.

The stairs are readily folded by swinging the sections 18 and i9upwardly over the section 17 and then by pushing upwardly on the freeend of the cover 24. The

out-of-line positions of the pivot pins 35 relative to the pivot pins 30and 37 permits the stair to swing upwardly with extremely limited force,and when the parts assume folded positions, they will be counterbalancedby the springs 43 to remain in folded positions.

From the foregoing it will be apparent that the construction isextremely simple and economical to manufacture. The simplicity of theconstruction makes it extremely rugged and long-lasting, as well asquiet in operation, and the structure has substantially unlimited life.

It is to be understood that the form of the invention illustrated is tobe taken as a preferred example of the same and that the scope of theinvention is limited only by the appended claims.

I claim:

1. A folding stairway comprising a rectangular open frame having end andside walls, a ladder hinged at one end to one end wall of said frame, abell crank lever having relatively long and relatively short armssubstantially at right angles to each other, a pivot pin connecting saidbell crank lever at the junction of said arms with one of said sidewalls, a first link pivotally connected at one end to the end of thelong arm of said bell crank lever and at its other end to said ladder, aspring assembly comprising a tension coil spring, means connecting oneend of said spring to said frame adjacent said one end wall, and asecond link connected at one end to the other end of said spring, saidlink being directly connected at its other end to the end of said shortarm of said bell crank lever, the points of connection of said secondlink with said short arm of said bell crank lever and with said otherend of said spring and the point of connection of said one end of saidspring with said frame lying in a straight line throughout the greaterportion of the movement of said bell crank lever between open and closedpositions of said ladder, said short arm of said bell crank leverprojecting generally away from said one end wall when said ladder is inlower position and projecting generally upwardly when said ladder is inclosed position, said straight line being substantially perpendicular tosaid short arm of said bell crank lever when said ladder is in closedposition, the point of connection of said second link with said otherend of said spring, when said ladder is in open position, lying betweensaid pivot pin and said one end wall, and a stationary elementengageable with said second link solely when said ladder approaches openposition to deflect said link slightly upwardly, a line between saidstationary element and the point of connection of said second link withsaid short arm of said bell crank lever being at a slight angle to aline between said pivot pin and the point of connection of said secondlink with said short arm of said bell crank ever to preserve in thelatter a relatively small moment arm acted on by said spring assembly totend to turn said bell crank lever about said pivot pin.

2. A folding stairway according to claim 1 wherein said stationary meanscomprises a relatively large head carried by said pivot pin, said headengaging said second link at a point intermediate the ends thereof andsupporting such point appreciably above the axis of said pivot pin.

3. A folding stairway comprising a rectangular open frame having end andside walls, a ladder hinged at one end to one end wall of said frame, abell crank lever having relatively long and relatively short armssubstantially at right angles to each other, a pivot pin connecting saidbell crank lever at the junction of said arms with one of said sidewalls, a first link pivotally connected at one end to the end of thelong arm of said bell crank lever and at its other end to said ladder, aspring assembly comprising a tension coil spring, means connecting oneend of said spring to said frame adjacent said one end wall, and asecond link connected at one end to the other end of said spring, saidlink being directly connected at its other end to the end of said shortarm of said bell crank lever, the points of connection of said secondlink with said short arm of said bell crank lever and with said otherend of said spring and the point of connection of said one end of saidspring with said frame lying in a straight line throughout the greaterportion of the movement of said bell crank lever between open and closedpositions of said ladder, said short arm of said bell crank leverprojecting generally away from said one end wall when said ladder is inlower position and projecting generally upwardly when said ladder is inclosed position, said straight line being substantially perpendicular tosaid short arm of said bell crank lever when said ladder is in closedposition, the point of connection of said second link with said otherend of said spring, when said ladder is in open position, lying betweensaid pivot pin and said one end wall, and a stationary elementengageable with said second link solely when said ladder approaches openposition to deflect said link slightly upwardly, said second link beingformed of relatively stiff material whereby the deflection of saidsecond link out of said straight line transmits to the end of said shortarm of said bell crank lever a force transversely thereof tending toturn said bell crank lever about said pivot pin.

4. A folding stairway according to claim 3 wherein said stationary meanscomprises a relatively large head carried by said pivot pin and engagingsaid second link at a point intermediate the ends thereof and supportingsuch point appreciably above the axis of said pivot pin.

5. A folding stairway according to claim 3 wherein a line between thepoint of engagement of said second link with said stationary means andthe point of connection of said second link with said short arm of saidbell crank lever is at a slight angle to a line between the axis of saidpivot pin and the point of connection of said second link with saidshort arm of said bell crank lever to preserve in said short arm arelatively short moment arm acted on by the tension of said springassembly to cooperate with said force transmitted transversely to saidshort arm of said bell crank lever to tend to turn said bell crank leverabout said pivot pin.

References Cited in the file of this patent UNITED STATES PATENTS320,692 Ready June 23, 1885 2,095,392 Marschke Oct. 12, 1937 2,506,380Myers May 2, 1950 2,649,237 Bjorklund et al. Aug. 20, 1953

